In has been previously proposed to use microprocessor-controlled electric-motor-driven fluid dispensers in which conventional syringe and piston assemblies (such as used in medical and related applications) are acted upon, under microprocessor control, to push the piston controlled distances into the fluid-filled syringe in order to dispense predetermined volume or size fluid droplets from the syringe, as through a terminal needle or the like. U.S. Pat. Nos. 5,630,527 and 5,765,722 (and patents referred to therein) are examples of such dispensers, as are the dispensing syringe pump systems of Cole-Parmer Instrument Company described in their 1993-4 Instruments Catalog, pages 1025-6. For purposes of uniformly depressing the piston of such conventional--syringe-and-piston assemblies, a movable or displaceable driving rod (such as a threaded rod) is moved through a central aperture in a fixed electric motor that drives the rod, to insert a plunger disposed at the end of the rod into the syringe and into flat engagement with the piston of the syringe and piston assembly, thereby to move the piston the desired amount into the syringe. Such techniques requiring a driven flat plunger to engage and then set in motion the stationary piston of the conventional syringe-and-piston assembly, however, has been found, in practice, to be subject to lag caused by the inertia in engaging and moving the syringe piston and starting the consequent expulsion of the fluid from the syringe, and subject to less than a very sharp, controlled cut-off--with limitations, also, on the smallest size droplets dispensable and the precise micro-control of the same.
It is to the obviating of such problems and limitations that the construction and operation of the present are directed, enabling a great improvement in the instantaneous dispensing and in the sharp, controlled cut-off, and with previously unattainable uniform micro-size droplets.